Studies on the etiology and significance of cemental caries as a dental problem will continue. The project will include laboratory studies on extracted teeth with root surface caries in order to characterize the bacterial flora involved. Representative bacterial isolates will be tested in suitable animal models to determine their pathogenic potential for cemental surfaces. Studies on the establishment and transmission of S. mutans and Actinomyces will be continued. Colonization patterns will be studied in different animal models including gnotobiotic rats and subhuman primates. In order to detect low numbers of organisms at the early stages of colonization, sensitive selective media will be employed. Priority will be placed on a suitable selective medium for Actinomyces. Comparative pathogenicity of the different species of Actinomyces isolated from the human mouth will be investigated. Transmission patterns of S. mutans and Actinomyces will be studied using bacteriocin production and sensitivity characteristics of the organisms. Possible role of bacteriocins as in vivo regulators of plaque ecology will be investigated. Feasibility of controlling S. mutans and Actinomyces populations in school children by the use of antibacterial compounds will be studied. Bacteriological studies will be coordinated with observations on caries incidence. Particular emphasis will be placed on tests of efficacy using profiles of significant bacteria.